In order to conduct more current, it is necessary to use wide metal lines for power rail applications. However, there are many hurdles to overcome in order to insert selective wide metal lines in a self-aligned double patterning (SADP) line array. This is due to all metal lines being printed and patterned in the same width and pitch in the SADP scheme. To overcome such obstacles, a complicated pattering scheme needs to be used which requires additional masks and fabrication processes. This results in significantly higher manufacturing complexity and costs.
More specifically, the width of metal lines is limited by the photolithography processes required by the SADP integration, used to pattern the trenches in the interlevel dielectric material. In SADP integration, for example, a mandrel is patterned by conventional lithography and etching processes. Spacers are formed on sidewalls of the patterned mandrel, with the patterned mandrel subsequently being removed through conventional etching processes. The removal of the mandrels results in the spacers being used as an etch mask for patterning of the underlying hard mask layer. The patterned hard mask layer is then used to etch trenches in the inter-metal dielectric material, which are filled with metal material to form the metal lines for power rail applications. But, due to the regular nature of the spacers, i.e., line width and spacing, it is not possible to form trenches with different widths, much less with widths greater than the width of the patterning process. The patterning of the wider lines, e.g., needed for high current capacity power rails, thus requires additional masking and patterning steps, resulting in increased fabrication complexity and cost.